Magnetic read/write system and magnetic recording medium

ABSTRACT

A novel magnetic read/write system, in which a fixed MR head serves to read magnetically recorded data from a magnetic recording medium as it operates at a relative speed of 2.0 to 5.0 m/s with respect to the magnetic recording medium comprising a non-magnetic support and a magnetic layer. A fatty acid ester represented by general formula (I):  
                 
 
     where R 1  is a hydrocarbon having 4 or less carbons, and R 2  is a straight-chain hydrocarbon having 12 or more carbons, exists between a read element of the MR head and the magnetic layer. This magnetic read/write system exhibits improved adherence to heads, running durability, and wear resistance of the tape in low temperature conditions as well as at room temperature.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic read/write systemthat uses a fixed MR head to read magnetically recorded data from amagnetic recording medium, and to such a magnetic recording medium. Moreparticularly, the present invention relates to a magnetic read/writesystem that employs a fixed MR head to read magnetically recorded datafrom a magnetic recording medium, with improved running durability,adherence to a head, and wear resistance and to such a magneticrecording medium.

[0003] 2. Description of the Related Art

[0004] As the recording density of magnetic recording media increases,friction between a magnetic layer and components of a reading deviceduring running has posed a significant problem and there is anincreasing need to improve running durability, adherence to a head, andwear resistance of such recording media.

[0005] To meet such needs, techniques have been developed where a fattyacid ester is added to a magnetic layer of a magnetic recording mediumthat is mainly composed of ferromagnetic powder and binder resin(Japanese Patent Laid-Open Publication No. Sho 50-22603, Japanese PatentLaid-Open Publication No. Sho 50-153905, Japanese Patent Laid-OpenPublication No. Sho 53-149302, Japanese Pent Laid-Open Publication No.Sho 55-139637, Japanese Patent Publication No. Sho 39-28367, JapanesePatent Publication No. Sho 41-18065, and Japanese Patent Publication No.Sho 47-12950).

[0006] These techniques, however, suffer a problem that many of theester compounds that have straight-chain alkyls, which bring about theirrelatively high lubricating performance, have high melting points andthus form deposits on the surface of the magnetic layer at lowtemperatures. To cope with this, some techniques employ a fatty acidester having a saturated or unsaturated branched hydrocarbon group withhigh molecular weight as an additive to the magnetic layer (JapanesePatent Publication No. Sho 47-12950, Japanese Patent Laid-OpenPublication No. Sho 58-218038, Japanese Patent Laid-Open Publication No.Sho 60-205827, Japanese Patent Laid-Open Publication No. Sho 61-294637,and Japanese Patent Laid-Open Publication No. Sho 62-125529). Onetechnique involves adding to the magnetic layer a fatty acid esterhaving the following general formula:

[0007] where R¹¹ is a straight-chain saturated alkyl having 6 to 12carbons, R¹² is a straight-chain saturated alkyl having 4 to 10 carbons,and R is a straight-chain or branched alkyl having 4 to 22 carbons(Japanese Patent No. 2559259).

[0008] One type of magnetic read/write system, which has recently beenput to practical use and is intended for use in a computer back-upsystem, reads data stored in a magnetic recording medium using a fixedMR head that operates at a relative speed of 2.0 to 5.0 m/s with respectto the recording medium. The system, known as the linear tape drivesystem, operates on the basis of linear scanning, in which a magnetictape (which may be referred to simply as a tape, hereinafter) is movedalong its length with respect to the fixed MR head as the data is readalong that direction. Unlike a helical scanning system, which employs arotary head, the magnetic tape is moved at high speeds in this system.As a result, the tape is vigorously rubbed against the head or guiderolls, causing the magnetic coating to come off the tape. For thisreason, the role of the lubricant has become ever more significant tominimize damage to the coating, and should the coating come off thetape, it is desirable that the coating does not stick to the surroundingarea of the head gap.

[0009] No conventional fatty acid ester has ever achieved satisfactoryperformance when added to the magnetic layer in such a system. Forexample, fatty acid esters that have a saturated or unsaturated branchedhydrocarbon with high molecular weight are less than satisfactory interms of film strength and lubricating performance of the magnetic layerunder low temperature conditions.

[0010] Fatty acid esters used in a magnetic disk as described inJapanese Patent No. 2559259 are less likely to crystallize and remain ina liquid state at relatively low temperatures, exhibiting lubricatingproperty. These fatty acid esters do not readily evaporate from thesurface of the magnetic layer at high temperatures, nor do they formdeposits at low temperatures since fatty acid units and alcohol unitspresent in the molecule have a limited number of carbons. Thus, thefatty acid esters are capable of providing high running durability undervarious conditions. However, the lubricating performance of these fattyacid esters is not sufficient because of their high dynamic viscosity.Therefore, a high friction results when the fatty acid esters areapplied to the tape. This causes abrasion of the coating.

[0011] The present invention addresses the above-identified problemsassociated with the prior art.

[0012] Accordingly, it is an objective of the present invention toprovide a magnetic read/write system that uses a fixed MR head to readmagnetically recorded data from a magnetic recording medium that hasimproved adherence to a head, running durability and wear resistanceunder low temperature conditions, as well as at room temperature, and toprovide such a magnetic recording medium. In particular, the presentinvention aims at provision of a magnetic read/write system that uses amagnetic tape exhibiting improved performances in terms of theabove-described adherence, running durability, and wear resistance whenused in a linear tape drive system, in which the fixed MR head readsmagnetically recorded data from a magnetic recording medium formed as atape (i.e., a magnetic tape), such as DLT4, while operating at arelative speed of 2.0 to 5.0 m/s with respect to the recording medium.It is also an objective of the present invention to provide such amagnetic tape.

SUMMARY OF THE INVENTION

[0013] In the course of their studies to find a solution to theabove-described problems, the present inventors have found that theabove-described objectives can be achieved by providing a non-magneticlayer that contains a specific fatty acid ester and a fatty acid betweena non-magnetic support and the above-described magnetic layer andultimately completed the present invention.

[0014] In one aspect, the present invention provides a magneticread/write system, in which a fixed MR head serves to read magneticallyrecorded data from a magnetic recording medium as it operates at arelative speed of 2.0 to 5.0 m/s with respect to the magnetic recordingmedium comprising a non-magnetic support and a magnetic layer, wherein afatty acid ester represented by general formula (I):

[0015] where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, exists between aread element of the MR head and the magnetic layer.

[0016] In another aspect, the present invention provides such a magneticrecording medium comprising:

[0017] a non-magnetic support;

[0018] a magnetic layer containing a ferromagnetic powder and a binderresin, the magnetic layer formed over the non-magnetic support andhaving a dry thickness of 0.5 μm; and

[0019] a non-magnetic layer containing a non-magnetic powder and abinder resin, the non-magnetic layer interposed between the non-magneticsupport and the magnetic layer, the non-magnetic layer containing as alubricant a fatty acid ester represented by general formula (I):

[0020] where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, and a fatty acidhaving 12 or more carbons.

[0021] The fatty acid ester of the general formula (I) for use with thepresent invention, which is derived from fatty acids having ahydrocarbon branch at 2′-position, has a low solidification point anddoes not suffer a significant decrease in the lubricity in lowtemperature conditions. In addition, this fatty acid ester has a shorterfatty acid side chain as compared to the conventional fatty acid estersas represented by the general formula (II) and thus exhibits low dynamicviscosity and shear viscosity even in low temperature conditions.Accordingly, by using the fatty acid ester, not only can the frictionand the wear in the tape be reduced in a wide temperature range, butalso the durability under various environments is improved. Furthermore,in terms of physical properties, the fatty acid ester exhibits lessoiliness, the property being characteristic of fatty acid esters. Thisis believed to contribute to the improvements in the adherence to a headand stickiness of the tape. In the present invention, the fatty acidester of the general formula (I) is added only to the non-magnetic layerand is allowed to gradually migrate from the non-magnetic layer throughthe magnetic layer to the surface thereof. In this manner, highdurability and wear-resistance can be achieved even when the tape ismoved at a relative speed of 2.0 to 5.0 m/s with respect to the fixed MRhead. These effects are not obtained if the fatty acid ester is addedonly to the magnetic layer. The concurrent presence of the fatty acidwith the non-magnetic powder in the non-magnetic layer makes it possiblefor the fatty acid ester to migrate in the manner described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will now be described in detail withreference to preferred embodiments.

[0023] <Non-Magnetic Support>

[0024] A non-magnetic support for use in a recording medium of thepresent invention is a sheet of film and is properly selected fromconventional resin films made of resin materials including, but notlimited to, polyesters, polyamides, or aromatic polyamides, or resinfilms formed by laminating these films. Such films, as well as itsthickness and other parameters, are known, and should not be limited toa particular one.

[0025] <Magnetic Layer>

[0026] Ferromagnetic powder contained in the magnetic layer of themagnetic recording medium of the present invention is a ferromagneticmetal powder that has a needle-like shape and preferably has an averagemajor axis length of 0.15 μm or less, more preferably from 0.05 to 0.10μm. If the powder has an average major axis length exceeding 0.15 μm,the electromagnetic conversion characteristics (in particular, S/N andC/N characteristics) required of magnetic recording media will becomeinsufficient.

[0027] Preferably, the ferromagnetic powder is contained in the magneticlayer composition in an amount of 70 to 90% by weight. If the amount ofthe ferromagnetic powder is excessively large, the amount of binder isreduced and, as a result, the surface smoothness of the recording mediumafter calendering worsens. Conversely, if the amount of theferromagnetic material is excessively small, high read output cannot beachieved.

[0028] Examples of the binder resin for use in the magnetic layerinclude, but are not limited to, conventional thermoplastic resins,thermosetting resins, radiation cure resins, and mixtures thereof.

[0029] Preferably, the binder resin is contained in the magnetic layerin an amount of 5 to 40 parts by weight, particularly 10 to 30 parts byweight with respect to 100 parts by weight of the ferromagnetic powder.If the amount of the binder resin is too small, the strength of themagnetic layer is reduced and running durability may be lowered. On theother hand, if the amount is too large, the amount of the ferromagneticmetal powder is reduced, resulting in a reduced electromagneticconversion characteristic.

[0030] When a thermosetting resin is used as the binder resin, variousknown polyisocyanates can be used to serve as a cross-linking agent forhardening the binder resin. The amount of the cross-linking agentcontained in the magnetic layer is preferably from 10 to 30 parts byweight with respect to 100 weight parts of the binder resin. Ifnecessary, abrasives, dispersing agents such as surface active agents,higher fatty acids and various other additives may be added to themagnetic layer.

[0031] A coating for forming the magnetic layer is prepared by adding anorganic solvent to the above-described components. The organic solventmay be one or more solvents properly selected from ketone solventsincluding methylethylketone (MEK), methylisobutylketone andcyclohexanone, and aromatic compound solvents including toluene. The useof other organic solvents is also contemplated. The amount of theorganic solvent to be added is preferably from about 100 to about 900parts by weight with respect to 100 parts by weight of the total amountof solid content (such as the ferromagnetic metal powder and variousinorganic particles) and the binder resin.

[0032] In the present invention, the magnetic layer has a thickness of0.50 μm or less, preferably from 0.05 to 0.50 μm, and more preferablyfrom 0.10 to 0.25 μm. The magnetic layer that is too thick may increasethe self-magnetization loss and thickness loss.

[0033] <Non-Magnetic Layer>

[0034] The magnetic recording medium of the present invention includes anon-magnetic layer interposed between the above-described magnetic layerand the non-magnetic support. In this manner, the electromagneticconversion characteristic of the thin-layered magnetic layer is enhancedand reliability of the recording medium is further improved.

[0035] One characteristic of the present invention resides in that thenon-magnetic layer contains as a lubricant a fatty acid esterrepresented by the following general formula:

[0036] where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons. Among such fattyacid esters, cetyl 2-ethylhexanoate, stearyl 2-ethylhexanoate, myristyl2-ethylhexanoate and stearyl 2-ethylbutanoate are preferred, with cetyl2-ethylhexanoate being particularly preferred.

[0037] By adding these fatty acid esters to the non-magnetic layer, theDLT4 durability as well as adherence to head can further be improved ascompared to using conventional fatty acid esters. Also, the decrease inthe durability due to discharge, which is seen when fatty acid esterswith melting points of 30° C. or higher are used, does not take place inrelatively low temperature environments. Also, the fatty acid esters ofthe present invention, serving as a lubricant, have a smaller dynamicviscosity and a shear viscosity due to their relatively shorter carbonchains than those of the conventional fatty acid esters. Accordingly,damage to the coating caused by the friction between the magnetic layerof the magnetic tape and a back-coat layer is reduced. If the fatty acidester having the general formula (I) has R¹ containing 5 or more carbonsor has its ethyl replaced with an alkyl with 3 or more carbons, thefatty acid ester becomes oily, which affects the adherence to a head andstickiness of the tape. If R³ has less than 12 carbons, the fatty acidester tends to crystallize in low temperature conditions and tends toevaporate from the surface of the magnetic layer in high temperatureconditions.

[0038] Preferably, the lubricant is blended in the non-magnetic layer inan amount of 0.2 to 5 parts by weight with respect to 100 weight partsof the non-magnetic powder. If the amount is less than 0.2 parts byweight, the desired effects cannot be achieved. If the amount exceeds 5parts by weight, improvements in the running durability or wearresistance of the tape are not as significant as expected from theamount. In addition, if the amount is excessive, significant problemsarise especially with tapes, such as reduced durability due to dischargeand the magnetic layer sticking to the back-coat layer.

[0039] The non-magnetic layer contains at least non-magnetic powder,binder resin, and fatty acid with 12 or more carbons and has a thicknessof preferably 2.5 μm or less, more preferably from 0.1 to 2.3 μm. Thethickness larger than 2.5 μm does not improve performance of thenon-magnetic layer any further. On the contrary, too large a thicknesscan often result in non-uniformity in thickness in a coating layer. Notonly does this require stricter coating conditions but also may resultin a reduced surface smoothness.

[0040] Various inorganic powders can be used as the non-magnetic powderfor use in the non-magnetic layer. For example, needle-shapednon-magnetic powders, such as needle-shaped non-magnetic iron oxide(α-Fe₂O₃), are preferably used. Various other non-magnetic powders,including calcium carbonate (CaCO₃), titanium oxide (TiO₂), bariumsulfate (BaSO₄), and α-alumina (α-Al₂O₃), may preferably be blended. Thenon-magnetic layer preferably contains a carbon black, example of whichincludes furnace black for rubber, thermal black for rubber, black forcolor and acetylene black.

[0041] The carbon black and the inorganic powder are preferably blendedat a ratio of 100:0 to 10:90 by weight. The proportion of the inorganicpowder greater than 90 may lead to a problem in terms of surfaceelectrical resistance.

[0042] As with the case of the magnetic layer, the binder resin may be aconventional thermoplastic resin, thermosetting resin, radiation cureresin and a mixture thereof, with the radiation cure resin beingparticularly preferred.

[0043] It is essential that the non-magnetic layer of the presentinvention further contain as an additive a fatty acid with 12 or morecarbons, preferably stearic acid. When necessary, it may further containa dispersing agent, such as a surface-active agent, and various otheradditives.

[0044] <Back-Coat Layer>

[0045] A back-coat layer is optionally provided for the purposes ofimproving running stability and preventing static electricity frombuilding up in the magnetic layer. The back-coat layer preferablycontains from 30 to 80% by weight of carbon black, which may be any ofcommonly used carbon blacks and may be the same as that used in thenon-magnetic layer. In addition to the carbon black, the back-coat layermay optionally contain non-magnetic inorganic powders, such as theabrasives used in the magnetic layer, a dispersing agent such as asurface-active agent, a lubricant such as higher fatty acid, fatty acidester and silicone oil, and various other additives.

[0046] The back-coat layer has a thickness of 0.1 to 1.0 μm, preferably0.2 to 0.8 μm (after calendering). The thickness greater than 1.0 μmresults in excessive friction between the recording medium and the paththat the recording medium follows and is rubbed against. This leads toreduced running stability. On the other hand, the thickness less than0.1 μm results in the back-coat layer being abraded as the recordingmedium is moved.

[0047] The above-described magnetic recording medium of the presentinvention has improved adherence to a head, running durability, and wearresistance of the tape and thus is suitable for use with fixed MR headsunder low temperature conditions as well as at room temperature. In anMR head, resistance of a read sensor, which uses a magnetic material,changes when the read sensor is exposed to magnetic field, which allowsthe MR head to read external magnetic signals. Output of an MR head isnot affected by the relative speed of the head with respect to therecording medium, and for this reason, MR heads can achieve high outputwhen used to read magnetically recorded data recorded with a high trackrecording density. In order to achieve high resolution and high RFcharacteristic, a typical MR head has a construction in which amagnetoresistive film (MR film) is interposed between a pair of magneticshield film (Shielded MR head).

[0048] In a preferred magnetic read/write system, data is first recordedmagnetically on the magnetic recording medium of the present inventionand the data is then read using a fixed MR head operated at a relativespeed of 2.0 to 5.0 m/s. The fatty acid ester of general formula (I)added to the non-magnetic layer of the magnetic recording medium isallowed to exist between the read element of the MR head and themagnetic layer.

EXAMPLES

[0049] The present invention will now be described with reference toexamples.

Example 1

[0050] <Coating 1 for forming non-magnetic layer> Needle-shaped α-Fe₂O₃70 parts by weight (DPN-250BW manufactured by TODA KOGYO Co., Ltd.)(Average minor axis diameter = 28 nm, BET = 55 m²/g) Carbon black (#850Bmanufactured 30 parts by weight by MITSUBISHI CHEMICAL Co., Ltd.)(Average particle size = 16 nm, BET = 200 m²/g, DBP oil absorbance = 70ml/100 g) α-Al₂O_(3 (HIT60A manufactured) 5.5 parts by weight bySUMITOMO CHEMICAL Co., Ltd.) (Average particle size = 0.18 μm, BET = 12m²/g) Electron beam-curable vinyl chloride copolymer 20 parts by weight(Degree of polymerization = 300, polar group: —OSO₃K = 1.5/molecule)Election beam-curable polyurethane resin 8 parts by weight (Mn = 25000,polar group: sodium hypophosphite = 1/molecule) MEK 120 parts by weightToluene 120 parts by weight Cyclohexanone 60 parts by weight

[0051] The above-listed components were mixed and kneaded and dispersedusing a sand grinder mill.

[0052] The following additives and solvents were then added to adjustviscosity. This completed the non-magnetic coating 1. Cetyl2-ethylhexanoate 2 parts by weight Stearic acid 1 parts by weight MEK 40parts by weight Toluene 40 parts by weight Cyclohexanone 40 parts byweight <Magnetic coating 1> Fe-based metal magnetic powder 100 parts byweight (containing 10 atm % Co and 5 atm % Al with respect to Fe (=100))(He = 144.6 kA/m, σs = 130 Am²/kg, BET 57 m²/g, average major axislength = 0.10 μm) Vinyl chloride copolymer 10 parts by weight (MR110manufactured by ZEON Co., Ltd) (Degree of polymerizalion = 300, polargroup: —OSO₃K = 1.5/molecule) SO₃Na-containing polyurethane resin 7parts by weight (Mn = 25000, polar group conc. = 1/molecule) α-Al₂O₃ 12parts by weight (HIT782 manufactured by SUMITOMO CHEMICAL Co., Ltd.)(Average particle size = 0.12 μm, BET = 20 m²/g) Myristic acid 2 partsby weight MEK 90 parts by weight Toluene 90 parts by weightCyclohexanone 120 parts by weight

[0053] The above-listed components were mixed and kneaded and dispersedusing a sand grinder mill.

[0054] The following solvents were then added to adjust viscosity,completing the magnetic coating 1. MEK 110 parts by weight Toluene 110parts by weight Cyclohexanone 160 parts by weight <Coating for formingback-coat layer> Carbon black 80 parts by weight (Conductex SCmanufactured by COLUMBIAN CARBON Co., Ltd., average patlicle size = 20nm, BET = 220 m²/g) Carbon black 1 parts by weight (Sevacarb MTmanufactured by COLUMBIAN CARBON Co., Ltd, average particle size = 350nm, BET = 8 m²g) α-Fe₂O₃ 1 parts by weight (TF100 manufactured by TODAKOGYO Co., Ltd, average particle size 0.1 μm) Vinyl chloride-vinylacetate-vinyl 65 parts by weight alcohol copolymer (Ratio by weight ofmonomers = 92:3:5, average degree of polymerization = 420)Polyesterpolyurethane resin 35 parts by weight (UR-8300 manufactured byTOYOBO Co., Ltd.) MEK 260 parts by weight Toluene 260 parts by weightCyclohexanone 260 parts by weight

[0055] The components above were mixed and kneaded and dispersed using asand grinder mill.

[0056] The following additives and solvents were then added to adjustviscosity. This completed the coating for forming the back-coat layer.MEK 210 parts by weight Toluene 210 parts by weight Cyclohexanone 210parts by weight <Preparation of magnetic tape>

[0057] The coating 1 for non-magnetic layer was applied onto one surfaceof a biaxially oriented, laminated PEN (polyethylene naphthalate) filmhaving a thickness of 6.2 μm. The coating was then dried and subjectedto calendering. Subsequently, an electron beam was irradiated (5 Mrad)onto the film in nitrogen atmosphere to harden the coating. The coating1 for magnetic layer was then applied on top of the non-magnetic layer,oriented, dried, and subjected to calendering. After calendering, themagnetic layer and the non-magnetic layer had thicknesses of 0.2 μm and1.8 μm, respectively. Subsequently, the coating for back-coat layer wasapplied to the opposite surface of the PEN film, dried, and subjected tocalendering. After calendering, the back-coat layer had a thickness of0.5 μm.

[0058] The film roll obtained in this manner was left for 24 hours atroom temperature and was then hardened in an oven for 24 hours at 60° C.The roll was then cut into ½ inch-wide tapes, which in turn were fittedin a cassette to make a sample magnetic tape.

Example 2

[0059] A sample magnetic tape was fabricated in the same manner as inExample 1 except that stearyl 2-ethylhexanoate was used in place ofcetyl 2-ethylhexanoate in the non-magnetic coating 1.

Example 3

[0060] A sample magnetic tape was fabricated in the same manner as inExample 1 except that myristyl 2-ethylhexanoate was used in place ofcetyl 2-ethylhexanoate in the non-magnetic coating 1.

Example 4

[0061] A sample magnetic tape was fabricated in the same manner as inExample 1 except that stearyl 2-ethylbutanoate was used in place ofcetyl 2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 1

[0062] A sample magnetic tape was fabricated in the same manner as inExample 1 except that cetyl 2-ethyldecanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 2

[0063] A sample magnetic tape was fabricated in the same manner as inExample 1 except that decyl 2-ethyldecanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 3

[0064] A sample magnetic tape was fabricated in the same manner as inExample 1 except that t-butyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 4

[0065] A sample magnetic tape was fabricated in the same manner as inExample 1 except that isocetyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 5

[0066] A sample magnetic tape was fabricated in the same manner as inExample 1 except that isobutyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 6

[0067] A sample magnetic tape was fabricated in the same manner as inExample 1 except that sec-butyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 7

[0068] A sample magnetic tape was fabricated in the same manner as inExample 1 except that stearic acid was not added to the non-magneticcoating 1.

Comparative Example 8

[0069] A sample magnetic tape was fabricated in the same manner as inExample 1 except that cetyl 2-ethylhexanoate was not added to thenon-magnetic coating 1 and two parts by weight of cetyl 2-ethylhexanoatewere added to the magnetic coating 1.

[0070] Each of the magnetic recording media obtained in Examples andComparative Examples were measured for the following properties.

[0071] (Running Durability)

[0072] Using a DLT-4000 drive manufactured by Quantum (relative speedbetween the fixed MR head and the magnetic tape=2.4 m/s), each tape wastested for the running durability by passing the tape 1,000,000 timesover the fixed MR head to read/write data from/to part of the tape atroom temperature (about 23° C., 50% RH) and at 10° C., 20% RH. The tapewas determined to be defective when the number of retry attempts of theread/write operation increased or when it was no longer possible toread/write from/to the tape before the number of the tape pass reached1,000,000 times.

[0073] (Degree of Coating Abrasion After the Layers Were Rubbed AgainstEach Other.)

[0074] Using a horizontal high-speed tensile tester, model no. HTB-Smanufactured by Island Industry, the magnetic layer and the back-coatlayer of the tape were repeatedly rubbed against one another and thelayers were observed for abrasion using an optical microscope.Measurements were taken at a temperature of 20° C. and humidity of 60%.For measurement, the tape was mounted on a first guide roll of theDLT-4000 drive with the back-coat layer facing outside and in contactwith the magnetic layer. The tape was passed 300 times over a distanceof 50 mm at a speed of 2000 mm/min with the applied load of 40 g and theholding angle of 90°. After the 300 passes, the magnetic layer and theback-coat layer were observed for the degree of abrasion. Ratings weregiven on a scale of A, B and C; where A=no abrasion, B=moderateabrasion, and C=considerable abrasion.

[0075] <Adherence to Head>

[0076] Using a DLT-4000 drive manufactured by Quantum, each sample tapewas run for 2400 cycles to read/write data both at room temperature(about 23° C., 50% RH) and at 10° C., 20% RH. Subsequently, adherence tothe head was observed using an optical microscope at ×100. Ratings weregiven on a scale of A, B and C; where A=no adhesion to the head,B=moderate adhesion to head, and C=adhesion to the entire surface of thehead.

[0077] The results are shown in Tables 1 to 3 below. TABLE 1 Fatty acidNumber of Number of DLT4 running Adherence ester in carbons carbons indurability (passes) to head non-magnetic in R¹ in R² in Rm 10° C.Coating Rm 10° C. layer formula (I) formula (I) temp. 20% abrasion temp.20% Ex.1 cetyl 4 16 1 million 1 million A A A 2-ethylhexanoate Ex.2stearyl 4 18 1 million 1 million A A B 2-ethylhexanoate Ex.3 myristyl 412 1 million 1 million B A A 2-ethylhexanoate Ex.4 stearyl 2 18 1million 1 million B A A 2-ethylbutanoate Comp.Ex.1 cetyl 8 16 Half a300,000 C A B 2-ethyldecanoate million Comp.Ex.2 decyl 4 10 ¾ million400,000 B A A 2-ethyldecanoate

[0078] TABLE 2 Fatty acid DLT4 running Adherence ester in durability(passes) to head non-mag- Rm 10° C. Coating Rm 10° C. netic layer temp.20% abrasion temp. 20% Comp.Ex.3 t-butyl- 700.000 300,000 B B Bsteareate Comp.Ex.4 isocetyl 350.000 200,000 B B C steareate Comp.Ex.5isobutyl 500,000 300,000 B A A steareate Comp.Ex.6 sec-butyl 500,000400,000 B A A steareate

[0079] TABLE 3 DLT4 running Adherence Non-magnetic durability (passes)to head powder in non- Rm 10° C. Coating Rm 10° C. magnetic layer temp.20% abrasion temp. 20% Ex.1 DPN-250BW 1 1 A A A (α-iron oxide, millionmillion needle-shaped) Comp. DPN-250BW 450,000 100,000 C B B Ex.7(α-iron oxide, needle-shaped) Comp. DPN-250BW 200,000  50,000 C C C Ex.8(α-iron oxide, needle-shaped)

[0080] As has been described thus far, the present invention provides amagnetic recording medium that exhibits improved adherence to heads,running durability, and wear resistance of the tape in low temperatureconditions as well as at room temperature. The magnetic recording mediumof the present invention is suitable for use in the magnetic read/writesystem employing a fixed MR head.

[0081] While presently preferred embodiments of the present inventionhave been described, it should be appreciated that various changes andmodifications may be made by those skilled in the art without departingfrom the scope of the invention as set forth in the appended claims.

What is claimed is:
 1. A magnetic read/write system, in which a fixed MRhead serves to read magnetically recorded data from a magnetic recordingmedium as it operates at a relative speed of 2.0 to 5.0 m/s with respectto the magnetic recording medium comprising a non-magnetic support and amagnetic layer, wherein a fatty acid ester represented by generalformula (I):

where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, exists between aread element of the MR head and the magnetic layer.
 2. The magneticread/write system according to claim 1, wherein the magnetic recordingmedium comprising: a non-magnetic supports; a magnetic layer containinga ferromagnetic powder and a binder resin, the magnetic layer formedover the non-magnetic support and having a dry thickness of 0.5 μm; anda non-magnetic layer containing a non-magnetic powder and a binderresin, the non-magnetic layer interposed between the non-magneticsupport and the magnetic layer, the non-magnetic layer containing as alubricant said fatty acid ester and a fatty acid having 12 or morecarbons.
 3. A magnetic recording medium comprising: a non-magneticsupport; a magnetic layer containing a ferromagnetic powder and a binderresin, the magnetic layer formed over the non-magnetic support andhaving a dry thickness of 0.5 μm; and a non-magnetic layer containing anon-magnetic powder and a binder resin, the non-magnetic layerinterposed between the non-magnetic support and the magnetic layer, thenon-magnetic layer containing as a lubricant a fatty acid esterrepresented by general formula (I):

where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, and a fatty acidhaving 12 or more carbons.